An important feature in athletic shoes, particularly in running shoes, is to provide for an extremely light-weight construction while at the same time provide for support of the foot and for cushioning of the foot as the foot contacts the ground under varying loads. It is known that a runner's foot contacting the ground engages the ground first with the heel, then with the side of the foot and then with the forefoot. The shock recorded at the heel and forefoot upon contacting the ground while running can be extremely high, on the order of 3 g's while the shock recorded in jumping sports, for example basketball, may be as high as 7 g's. Because, particularly in the case of running shoes, the time that the heel contacts the ground is less than that when the forefoot contacts the ground, the intensity of the shock recorded by the heel is greater than that recorded by the forefoot. While prior art shoe constructions have included shock absorbing portions, such portions have not been placed in the area of the shoe subjected only to shock, or have the prior art constructions taken into account that the shock load varies over different areas of the sole portion of a shoe, or even that shock loads will vary due to the particular exercise for which the shoe is designed, i.e. basketball shoes compared with running shoes.
Heretofore athletic shoes have included various sole constructions having flexible nubs positioned evenly across the bottom of the sole. This results in an excess of nubs, and thus weight, in areas of the sole subjected to low g loading, as for example the inside of the arch area of the sole and, in some instances, results in not enough nubs being positioned in high load bearing areas. This is evidenced in that the few nubs positioned in high load bearing areas quickly wear due to uneven load distribution both in the vertical compression direction and in the horizontal shear direction. Further the nubs that have been used on athletic shoes to date have failed to take into account the need of placement and design of the nubs so as to facilitate easy flexing of the sole along lines which correspond to the joints of the foot of the wearer. This is an extremely important feature in running where it is important that as little effort and energy as possible be expended in flexing of the sole of the shoe.
It is therefore an object of our invention to provide for an athletic shoe construction that will be extremely light in weight but which at the same time will provide sufficient shock absorbing portions at those areas of the sole portion of the shoe subjected to shock loads and which also will compensate for differences in shock loads occurring between various area of the sole portion. In addition it is an object of the invention to provide for a tread design including placement and configuration of nubs on the outer sole of the shoe to provide a minimum weight penalty while providing additional cushioning features and easy flexing of the sole portion.